Strengthened glass, strengthened glass plate, strengthened glass container, and glass for strengthening

ABSTRACT

To devise a tempered glass and a glass to be tempered each of which is lowered in density and viscosity at high temperature, hardly deteriorates a KNO 3  molten salt, and is excellent in thermal shock resistance. The tempered glass having a compression stress layer in a surface thereof, including as a glass composition, in terms of mol %, 50 to 80% of SiO 2 , 5 to 30% of Al 2 O 3 , 0 to 2% of Li 2 O, 5 to 25% of Na 2 O, and 0 to 5% of K 2 O, and being substantially free of As 2 O 3 , Sb 2 O 3 , PbO, and F.

TECHNICAL FIELD

The present invention relates to a tempered glass, a tempered glasssheet, and a glass to be tempered, in particular, to a tempered glass, atempered glass sheet, and a glass to be tempered suitable for a coverglass for a cellular phone, a digital camera, a personal digitalassistant (PDA), or a solar battery, or a glass substrate for a display,in particular, a touch panel display. Further, the present inventionrelates to a tempered glass container, in particular, a tempered glasscontainer for use as a container for pharmaceuticals.

BACKGROUND ART

Devices such as a cellular phone, a digital camera, a PDA, a touch paneldisplay, a large-screen television, and contact-less power transfer showa tendency of further prevalence.

A tempered glass, which is produced by applying tempering treatment toglass through ion exchange treatment or the like, is used for thoseapplications (see Patent Literature 1 and Non Patent Literature 1).

In addition, in recent years, the tempered glass has been more and morefrequently used in exterior parts of, for example, digital signage,mice, and smartphones.

A related-art device includes a display module, a touch panel sensor,and the tempered glass (protective member). In recent years, a methodinvolving forming the touch panel sensor on the tempered glass hasstarted to be adopted in order to achieve a reduction in weight or areduction in thickness. As a result, such protective member is requiredto: (1) have high mechanical strength; (2) have high flaw resistance;(3) be less costly; (4) have low density; (5) have sufficiently highacid resistance for preventing denaturation of its surface in acidtreatment at the time of formation of the touch panel sensor; and (6) befree of a substance having a high environmental load.

CITATION LIST Patent Literature

-   [PTL 1] JP 2006-83045 A

Non Patent Literature

-   [NPL 1] Tetsuro Izumitani et al., “New glass and physical properties    thereof,” First edition, Management System Laboratory. Co., Ltd.,    Aug. 20, 1984, p. 451-498

SUMMARY OF INVENTION Technical Problem

Incidentally, when the content of Li₂O in a glass composition isincreased, viscosity at high temperature can be lowered while ionexchange performance is enhanced. However, when the content of Li₂O isincreased and ion exchange treatment is performed using a potassiumnitrate molten salt (KNO₃ molten salt), a Li ion is liable to be mixedin the KNO₃ molten salt. The KNO₃ molten salt having mixed therein theLi ion makes it difficult to enhance the tempering characteristic of aglass to be tempered. As a result, the KNO₃ molten salt needs to befrequently replaced, and hence the productivity of a tempered glass isliable to lower. Further, when the content of Li₂O is increased,liquidus viscosity is liable to lower. It should be noted that a Na ionalso has property of deteriorating the KNO₃ molten salt, but the degreeof the deterioration is lower than that in the case of the Li ion.

In addition, hitherto, as the glass to be tempered, there has beenproposed a glass containing large amounts of Na₂O and K₂O in its glasscomposition. However, Na₂O and K₂O are each a component that increasesdensity. Meanwhile, when the contents of Na₂O and K₂O are decreased inorder to lower the density, the viscosity at high temperature increases,with the result that the productivity of the glass is liable to lower.Thus, it has been difficult to lower both the density and the viscosityat high temperature.

Further, as the content of Li₂O, Na₂O, or K₂O increases, the thermalexpansion coefficient of the glass to be tempered is liable to becomehigher. In addition, the ion exchange treatment is generally performedby immersing the glass to be tempered in a high-temperature (forexample, from 300 to 500° C.) KNO₃ molten salt. Thus, when the Li₂O,Na₂O, or K₂O-rich glass is subjected to ion exchange treatment, thetempered glass is liable to undergo breakage owing to a thermal shockwhen the glass to be tempered is immersed in the KNO₃ molten salt orwhen the tempered glass is taken out.

In order to solve the problem, it is conceivable to employ a methodinvolving preheating a glass sheet to be tempered before immersion inthe KNO₃ molten salt, or annealing a tempered glass that has been takenout of an ion exchange tank. However, such method requires a long periodof time, and hence involves a risk that the manufacturing cost of thetempered glass may soar.

The present invention has been made in view of the above-mentionedcircumstances, and a technical object of the present invention is todevise a tempered glass and a glass to be tempered each of which islowered in density and viscosity at high temperature, hardlydeteriorates an ion exchange solution, in particular, a KNO₃ moltensalt, and is excellent in thermal shock resistance.

Solution to Problem

The inventors of the present invention have made various studies, and asa result, have found the following. When, in a glass composition, thecontents of Al₂O₃ and Na₂O are increased, and at the same time, thecontents of Li₂O and K₂O are decreased, and as required, B₂O₃ isintroduced and the content of MgO is decreased, while ion exchangeperformance does not lower, density and viscosity at high temperaturelower, property of deteriorating an ion exchange solution lowers, andthermal shock resistance improves. The finding is proposed as thepresent invention. Thus, the finding is proposed as the presentinvention. That is, a tempered glass of the present invention has acompression stress layer in a surface thereof, comprises as a glasscomposition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and issubstantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein, the gist of thephrase “substantially free of As₂O₃” resides in that As₂O₃ is not addedpositively as a glass component, but contamination with As₂O₃ as animpurity is allowable. Specifically, the phrase means that the contentof As₂O₃ is less than 0.1 mol %. The gist of the phrase “substantiallyfree of Sb₂O₃” resides in that Sb₂O₃ is not added positively as a glasscomponent, but contamination with Sb₂O₃ as an impurity is allowable.Specifically, the phrase means that the content of Sb₂O₃ is less than0.1 mol %. The gist of the phrase “substantially free of PbO” resides inthat PbO is not added positively as a glass component, but contaminationwith PbO as an impurity is allowable. Specifically, the phrase meansthat the content of PbO is less than 0.1 mol %. The gist of the phrase“substantially free of F” resides in that F is not added positively as aglass component, but contamination with F as an impurity is allowable.Specifically, the phrase means that the content of F is less than 0.1mol %. It should be noted that when substantial addition of As₂O₃,Sb₂O₃, PbO, and F is eliminated, a closely related environmentalrequirement can be satisfied.

The tempered glass of the present invention preferably comprises as aglass composition, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 0.1 to2.5% of MgO, and 0 to 2.5% of MgO+CaO+SrO+BaO, and is preferablysubstantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein, the term“MgO+CaO+SrO+BaO” means the total amount of MgO, CaO, SrO, and BaO.

The tempered glass of the present invention preferably comprises as aglass composition, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 0.01 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, and 0.1 to2.5% of MgO+CaO+SrO+BaO, and is preferably substantially free of As₂O₃,Sb₂O₃, PbO, and F. Herein, the term “Li₂O+Na₂O+K₂O” means the totalamount of Li₂O, Na₂O, and K₂O.

The tempered glass of the present invention preferably comprises as aglass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 1 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5%of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5 of MgO, 0.1 to 2.5% ofMgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, andis preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F. Herein,the term “Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO” means the total amount of Li₂O,Na₂O, K₂O, MgO, CaO, SrO, and BaO.

The tempered glass of the present invention preferably comprises as aglass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5%of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% ofMgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO,preferably has a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from0.01 to 0.2, and is preferably substantially free of As₂O₃, Sb₂O₃, PbO,and F.

The tempered glass of the present invention preferably comprises as aglass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5%of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% ofMgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO,preferably has a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from0.01 to 0.2 and a molar ratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30,and is preferably substantially free of As₂O₃, Sb₂O₃, PbO, and F.Herein, the term “Al₂O₃+B₂O₃” means the total amount of Al₂O₃ and B₂O₃.

The tempered glass of the present invention preferably has a density of2.45 g/cm³ or less. Herein, the “density” can be measured by, forexample, a known Archimedes method.

When the tempered glass of the present invention is immersed in a 10mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, it ispreferred that a mass reduction be 40 mg/cm² or less. Herein, the “massreduction” is a mass reduction after immersion in the aqueoushydrochloric acid solution for 24 hours, and can be calculated by: firstmeasuring the mass and surface area of an evaluation sample before itsimmersion in the aqueous hydrochloric acid solution; then measuring themass of the evaluation sample after its immersion in the aqueoushydrochloric acid solution; and finally substituting the measured valuesinto the following expression: (mass before immersion-mass afterimmersion)/(surface area before immersion).

In the tempered glass of the present invention, it is preferred that acompression stress value of the compression stress layer be 300 MPa ormore, and a thickness of the compression stress layer be 10 μm or more.Herein, the “compression stress value of the compression stress layer”and the “thickness of the compression stress layer” refer to valuescalculated from the number of interference fringes and intervalstherebetween, the interference fringes being observed when a sample isobserved using a surface stress meter (for example, FSM-6000manufactured by TOSHIBA CORPORATION).

The tempered glass of the present invention preferably has a liquidustemperature of 1,200° C. or less. Herein, the phrase “liquidustemperature” refers to a temperature at which crystals of glass aredeposited after glass powder that passes through a standard 30-meshsieve (sieve opening: 500 μm) and remains on a 50-mesh sieve (sieveopening: 300 μm) is placed in a platinum boat and then kept for 24 hoursin a gradient heating furnace.

The tempered glass of the present invention preferably has a liquidusviscosity of 10^(4.0) dPa·s or more. Herein, the phrase “liquidusviscosity” refers to a value obtained through measurement of a viscosityof glass at the liquidus temperature by a platinum sphere pull upmethod.

The tempered glass of the present invention preferably has a temperatureat 10^(4.0) dPa·s of 1,300° C. or less. Herein, the phrase “temperatureat 10^(4.0) dPa·s” refers to a value obtained through measurement by aplatinum sphere pull up method.

The tempered glass of the present invention preferably has a thermalexpansion coefficient in a temperature range of from 30 to 380° C. of90×10⁻⁷/° C. or less. Herein, the phrase “thermal expansion coefficientin a temperature range of from 30 to 380° C.” refers to a value obtainedby measuring an average thermal expansion coefficient with adilatometer.

A tempered glass sheet of the present invention preferably comprises anyone of the tempered glasses.

The tempered glass sheet of the present invention preferably has alength dimension of 500 mm ox more, a width dimension of 300 mm or more,and a thickness of from 0.1 to 2.0 mm.

The tempered glass sheet of the present invention is preferably formedby an overflow down-draw method. Herein, the “overflow down-draw method”refers to a method comprising causing a molten glass to overflow fromboth sides of a heat-resistant forming trough, and subjecting theoverflowing molten glasses to down-draw downward while the moltenglasses are joined at the lower end of the forming trough, to therebymanufacture a glass sheet. In the overflow down-draw method, surfacesthat are to serve as the surfaces of the glass sheet are formed in astate of free surfaces without being brought into contact with thesurface of the forming trough. Accordingly, a glass sheet havingsatisfactory surface quality in an unpolished state can be manufacturedat low cost.

The tempered glass sheet of the present invention is preferably used fora touch panel display.

The tempered glass sheet of the present invention is preferably used fora cover glass for a cellular phone.

The tempered glass sheet of the present invention is preferably used fora cover glass for a solar battery.

A tempered glass sheet of the present invention is a tempered glasssheet having a length dimension of 500 mm or more, a width dimension of300 mm or more, and a thickness of from 0.1 to 2.0 mm, characterized inthat: the tempered glass sheet comprises as a glass composition, interms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% ofB₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5%of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO,and 13 to 1.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, has a molar ratioMgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molarratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and is substantially freeof As₂O₃, Sb₂O₃, PbO, and F; and the tempered glass sheet has a densityof 2.45 g/cm³ or less, a compression stress value of a compressionstress layer of 300 MPa or more, a thickness of the compression stresslayer of 10 μm or more, a liquidus temperature of 1,200° C. or less, anda thermal expansion coefficient in a temperature range of from 30 to380° C. of 90×10⁻⁷ or less.

A tempered glass container of the present invention comprises thetempered glass. Further, the tempered glass container of the presentinvention is preferably used for a container for pharmaceuticals.

As a container to be filled for storing a pharmaceutical, there has beenused a glass container in the form of an ampule, a vial, a prefilledsyringe, a cartridge, or the like. In recent years, along with progressin pharmacy and medicine, the number of cases where the glass containeris filled with an expensive drug has been increasing. However, the glasscontainer may break in a manufacturing process at a pharmaceuticalcompany, or at a clinical site. When the glass container filled with anexpensive drug breaks, not only the loss of the drug itself, but also aproduction loss involved in the interruption of a manufacturing lineoccurs, resulting in an extremely significant total loss in cost.Further, the breakage of the glass container also generates a safetyrisk.

A flaw present in the glass container is a cause for the breakage of theglass container. The flaw is generated in each of various steps such ascontainer processing, inspection, transportation, and drug filling.Therefore, the glass container to be used for a pharmaceutical isrequired to have flaw resistance, and because of the nature of itsapplication, is also required to have acid resistance and be free of anenvironmental load substance. Accordingly, the tempered glass (temperedglass container) of the present invention, which is excellent in flawresistance and acid resistance, and is substantially free of As₂O₃,Sb₂O₃, PbO, and F, is suitable for this application.

A glass to be tempered of the present invention preferably comprises asa glass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% ofAl₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5% of K₂O, and ispreferably substantially free of As₂O₃, Sb₂O₃, PbO, and F.

When the tempered glass of the present invention is immersed in a 10mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, it ispreferred that a mass reduction be 40 mg/cm² or less.

The glass to be tempered of the present invention preferably has a ratioCS₂/CS₁ of a compression stress value CS₂ to a compression stress valueCS₁ of 0.7 or more, the compression stress value CS₁ being determinedfor a compression stress layer that is obtained by subjecting the glassto be tempered to ion exchange treatment in a potassium nitrate moltensalt free of a history of being used, the compression stress value CS₂being determined for a compression stress layer that is obtained bysubjecting the glass to be tempered to ion exchange treatment in apotassium nitrate molten salt comprising 20,000 ppm (by mass) of Naions. It should be noted that in the calculation of the CS₂/CS₁, an ionexchange temperature is set to 430° C. and an ion exchange time is setto 4 hours.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1a is a schematic plan view illustrating a first example of theattachment state of a protective resin film with respect to a glasssheet to be tempered according to an embodiment of the presentinvention.

FIG. 1b is a schematic plan view illustrating a second example of theattachment state of the protective resin film with respect to the glasssheet to be tempered according to the embodiment of the presentinvention.

FIG. 1c is a schematic plan view illustrating a third example of theattachment state of the protective resin film with respect to the glasssheet to be tempered according to the embodiment of the presentinvention.

FIG. 1d is a schematic plan view illustrating a fourth example of theattachment state of the protective resin film with respect to the glasssheet to be tempered according to the embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS

A tempered glass of the present invention has a compression stress layerin a surface thereof. A method of forming the compression stress layerin the surface includes a physical tempering method and a chemicaltempering method. The tempered glass of the present invention ispreferably produced by the chemical tempering method.

The chemical tempering method is a method involving introducing alkaliions each having a large ion radius into the surface of glass by ionexchange treatment at a temperature equal to or lower than a strainpoint of the glass. When the chemical tempering method is used to form acompression stress layer, the compression stress layer can be properlyformed even in the case where the thickness of the glass is small. Inaddition, even when a tempered glass is cut after the formation of thecompression stress layer, the tempered glass does not easily breakunlike a tempered glass produced by applying a physical tempering methodsuch as an air cooling tempering method.

Described below are reasons why the content ranges of the respectivecomponents in the tempered glass of the present invention are restrictedas described above. It should be noted that in the description of thecontent range of each component, the expression “%” means “mol.” unlessotherwise specified.

SiO₂ is a component that forms a network of glass, and the content ofSiO₂ is from 50 to 80%, and is preferably from 55 to 77%, from 57 to75%, from 58 to 74%, from 60 to 73%, or from 62 to 72%. When the contentof SiO₂ is too small in glass, vitrification does not occur easily, theacid resistance of the glass reduces, the thermal expansion coefficientbecomes too high, and the thermal shock resistance easily lowers. On theother hand, when the content of SiO₂ is too large in glass, themeltability and formability easily lower, and the thermal expansioncoefficient becomes too low, with the result that it becomes difficultto match the thermal expansion coefficient with those of peripheralmaterials. It should be noted that when the content of SiO₂ is decreasedand the content of B₂O₃ is increased, density and viscosity at hightemperature can both be easily lowered, but at the same time, the acidresistance lowers, and hence it is difficult to apply the tempered glassto an acid treatment step at the time of the formation of a touch panelsensor.

Al₂O₃ is a component that enhances the ion exchange performance of glassand a component that enhances the strain point or Young's modulus, andthe content of Al₂O₃ is from 5 to 30%. When the content of Al₂O₃ is toosmall in glass, the ion exchange performance may not be exhibitedsufficiently. Thus, a suitable lower limit range of the content of Al₂O₃is 5.5% or more, 6% or more, 6.5% or more, 7% or more, 8% or more, or 9%or more. On the other hand, when the content of Al₂O₃ is too large inglass, the density of the glass easily increases and devitrifiedcrystals are easily deposited in the glass, and it becomes difficult toform a glass sheet by an overflow down-draw method or the like. Further,the thermal expansion coefficient of the glass becomes too low, and itbecomes difficult to match the thermal expansion coefficient with thoseof peripheral materials. In addition, the acid resistance also lowers,which makes it difficult to apply the tempered glass to an acidtreatment step at the time of the formation of a touch panel sensor.Further, viscosity at high temperature increases, which is liable tolower meltability. Thus, a suitable upper limit range of the content ofAl₂O₃ is 25% or less, 20% or less, 18% or less, 16% or less, 15% orless, 14% or less, 13.5% or less, 13.4% or less, 13% or less, 12.5% orless, or 12.4% or less.

Li₂O is an ion exchange component and is a component that lowers theviscosity at high temperature of glass to increase the meltability andthe formability, and increases the Young's modulus. However, Li₂O is acomponent that deteriorates an ion exchange solution. Further, Li₂O hasa great effect of increasing the compression stress value of glass amongalkali metal oxides, but when the content of Li₂O becomes extremelylarge in a glass system containing Na₂O at 7% or more, the compressionstress value tends to lower contrarily. Further, when the content ofLi₂O is too large in glass, the liquidus viscosity lowers, easilyresulting in the devitrification of the glass, and the thermal expansioncoefficient becomes too high, with the result that the thermal shockresistance lowers and it becomes difficult to match the thermalexpansion coefficient with those of peripheral materials. In addition,the viscosity at low temperature of the glass becomes too low, and thestress relaxation occurs easily, with the result that the compressionstress value lowers contrarily in some cases. Thus, the content of Li₂Ois 2% or less, and is preferably 1.7% or less, 1.5% or less, 1% or less,less than 1%, 0.5% or less, 0.3% or less, 0.2% or less, or 0.1% or less.

Na₂O is an ion exchange component and is a component that lowers theviscosity at high temperature of glass to increase the meltability andformability. Na₂O is also a component that improves the devitrificationresistance of glass. When the content of Na₂O is too small in glass, themeltability lowers, the thermal expansion coefficient unreasonablylowers, and the ion exchange performance is liable to lower. Thus, thecontent of Na₂O is 5% or more, and a suitable lower limit range thereofis 7% or more, more than 7.0%, 8% or more, or 9% or more. On the otherhand, when the content of Na₂O is too large in glass, there is atendency that the density increases and the thermal expansioncoefficient becomes too high, with the result that the thermal shockresistance lowers, it becomes difficult to match the thermal expansioncoefficient with those of peripheral materials, and the densityincreases. Further, the strain point lowers excessively, and the glasscomposition loses its component balance, with the result that thedevitrification resistance lowers contrarily in some cases. Further, theion exchange solution is liable to deteriorate. Thus, the content ofNa₂O is 25% or less, and a suitable upper limit range thereof is 23% orless, 21% or less, 19% or less, 18.5% or less, 17% or less, 16% or less,15.5% or less, 14% or less, 13.5% or less, or 13% or less.

K₂O is a component that promotes ion exchange and is a component thatallows the thickness of a compression stress layer to be easily enlargedamong alkali metal oxides. K₂O is also a component that lowers theviscosity at high temperature of glass to increase the meltability andformability. K₂O is also a component that improves devitrificationresistance. However, when the content of K₂O is too large, the densityof glass increases, the thermal expansion coefficient of the glassbecomes too large, the thermal shock resistance of the glass lowers, andit becomes difficult to match the thermal expansion coefficient withthose of peripheral materials. Further, the strain point lowersexcessively, and the glass composition loses its component balance, withthe result that the devitrification resistance tends to lowercontrarily. Thus, a suitable upper limit range of the content of K₂O is5% or less, 4% or less, 3.5% or less, or 3% or less. It should be notedthat when K₂O is added, a suitable addition amount is 0.1% or more, 0.5%or more, or 1% or more. In addition, when the addition of KO is avoidedas much as possible, the suitable addition amount is 1.9% or less, 1.35%or less, 1% or less, or less than 1%, particularly preferably 0.05% orless.

When the content of Li₂O+Na₂O+K₂O is excessively low, the ion exchangeperformance and the meltability are liable to lower. Thus, a suitablelower limit range of the content of Li₂O+Na₂O+K₂O is 5% or more, 9% ormore, 10% or more, 11% or more, 12% or more, 131 or more, or 14% ormore. On the other hand, when the content of Li₂O+Na₂O+K₂O isexcessively high, there is a tendency that the thermal expansioncoefficient increases excessively, with the result that the thermalshock resistance lowers, it becomes difficult to match the thermalexpansion coefficient with those of peripheral materials, and thedensity increases. There is also a tendency that the strain point lowersexcessively and the component balance of the glass composition is lost,with the result that the devitrification resistance lowers contrarily.Thus, a suitable upper limit range of the content of Li₂O+Na₂O+K₂O is30% or less, 19% or less, 18.5 or less, 18% or less, 17.5% or less, 17%or less, or 16.5% or less.

For example, the following components other than the components may beadded.

The content of B₂O₃ is preferably from 0 to 15%. B₂O₃ is a componentthat lowers the viscosity at high temperature and density of glass,stabilizes the glass so that a crystal may be unlikely precipitated, andlowers the liquidus temperature of the glass. In addition, B₂O₃ is acomponent that enhances crack resistance to enhance flaw resistance.Thus, a suitable lower limit range of the content of B₂O₃ is 0.01% ormore, 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, 4%or more, 5′% or more, 5.5% or more, or 6% or more. However, when thecontent of B₂O₃ is too large, the acid resistance of glass may reduce,coloring on the surface of the glass called weathering may occur throughion exchange, water resistance may lower, and the thickness of acompression stress layer is liable to decrease. Thus, a suitable upperlimit range of the content of B₂O₃ is 14% or less, 13% or less, 12% orless, 11% or less, less than 10.5%, 10% or less, 9% or less, or 8% orless.

MgO is a component that reduces the viscosity at high temperature ofglass to enhance the meltability and formability, and increases thestrain point and Young's modulus, and is a component that has a greateffect of enhancing the ion exchange performance among alkaline earthmetal oxides. Thus, a suitable lower limit range of the content of MgOis 0.01% or more, 0.05% or more, or 0.1% or more, particularlypreferably 0.5% or more. However, when the content of MgO is too largein glass, the density and thermal expansion coefficient easily increase,and the devitrification of the glass tends to occur easily. Thus, asuitable upper limit range of the content of MgO is 3% or less, 2.7% orless, 2.5% or less, 2.2% or less, 2% or less, 1.5% or less, or 1% orless.

CaO has greater effects of reducing the viscosity at high temperature ofglass to enhance the meltability and formability, and increasing thestrain point and Young's modulus without involving a reduction indevitrification resistance as compared to other components. However,when the content of CaO is too large in glass, the density and thermalexpansion coefficient increase, and the glass composition loses itscomponent balance, with the result that the glass is liable to devitrifycontrarily, the ion exchange performance lowers, and the deteriorationof an ion exchange solution occurs easily. Thus, the content of CaO ispreferably from 0 to 6%, from 0 to 5%, from 0 to 4%, from 0 to 3.5, from0 to 3%, from 0 to 2%, or from 0 to 1.

SrO is a component that reduces the viscosity at high temperature ofglass to enhance the meltability and formability, and increases thestrain point and Young's modulus. However, when the content thereof istoo large in glass, an ion exchange reaction is liable to be inhibited,and moreover, the density and thermal expansion coefficient increase,and the devitrification of the glass occurs easily. Thus, the content ofSrO is preferably from 0 to 1.5%, from 0 to 1%, from 0 to 0.5%, from 0to 0.1%, or from 0 to less than 0.1%.

BaO is a component that reduces the viscosity at high temperature ofglass to enhance the meltability and formability, and increases thestrain point and Young's modulus. However, when the content of BaO istoo large in glass, an ion exchange reaction is liable to be inhibited,and moreover, the density and thermal expansion coefficient increase,and the devitrification of the glass occurs easily. Thus, the content ofBaO is preferably from 0 to 6%, from 0 to 3%, from 0 to 1.5%, from 0 to1%, from 0 to 0.5%, from 0 to 0.1%, or from 0 to less than 0.1%.

When the content of MgO+CaO+SrO+BaO is excessively high, there is atendency that the density and the thermal expansion coefficientincrease, the glass devitrifies, and the ion exchange performancelowers. Thus, a suitable upper limit range of the content ofMgO+CaO+SrO+BaO is 9.9% or less, 6.5% or less, 5% or less, 3% or less,2.8% or less, 2.7% or less, 2.5% or less, 2.2% or less, 2% or less, 1.5%or less, or 1% or less. On the other hand, when the content ofMgO+CaO+SrO+BaO is excessively low, the meltability and the formabilityare liable to lower, and the strain point and the Young's modulus areliable to lower. Thus, a suitable lower limit range of the content ofMgO+CaO+SrO+BaO is 0.01% or more, 0.05% or more, 0.1% or more, or 0.5%or more.

When the content of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is excessively low,the meltability is liable to lower. Thus, a suitable lower limit rangeof the content of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is 10% or more, 12% ormore, 13% or more, or 14% or more. On the other hand, when the contentof Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is excessively high, there is atendency that the density and the thermal expansion coefficientincrease, and the ion exchange performance lowers. Thus, a suitableupper limit range of the content of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is 30%or less, 25% or less, 23% or less, 21% or less, 20% or less, 19% orless, 18.5% or less, or 18% or less.

When a molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) reduces, the ionexchange performance tends to lower, and the thermal expansioncoefficient is liable to increase. Thus, a suitable lower limit range ofthe molar ratio MgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) is 0.001 or more,0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more,or 0.05 or more. On the other hand, when the molar ratioMgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) increases, the devitrificationresistance is liable to lower, and the glass is liable to undergo phaseseparation. Thus, a suitable upper limit range of the molar ratioMgO/(Li₂O+Na₂O+K?O+MgO+CaO+SrO+BaO) is 0.5 or less, 0.3 or less, 0.25 orless, 0.2 or less, 0.15 or less, 0.1 or less, 0.09 or less, 0.08 orless, or 0.07 or less.

When a molar ratio (Al₂O₃+B₂O₃)/SiO₂ reduces, the crack resistance isliable to lower, and the meltability and the formability are liable tolower. Thus, a suitable lower limit range of the molar ratio(Al₂O₃+B₂O₃)/SiO₂ is 0.1 or more, 0.15 or more, 0.16 or more, 0.17 ormore, 0.18 or more, 0.19 or more, or 0.2 or more. On the other hand,when the molar ratio (Al₂O₃+B₂O₃)/SiO₂ increases, the devitrificationresistance is liable to lower, the glass is liable to undergo phaseseparation, and the acid resistance is liable to lower. Thus, a suitableupper limit range of the molar ratio (Al₂O₃+B₂O₃)/SiO₂ is 0.5 or less,0.4 or less, 0.35 or less, 0.32 or less, 0.31 or less, 0.30 or less,0.29 or less, 0.28 or less, 0.27 or less, or 0.26 or less.

A molar ratio B₂O₃/Al₂O₃ is preferably from 0 to 1, from 0.1 to 0.6,from 0.12 to 0.5, from 0.142 to 0.37, from 0.15 to 0.35, from 0.18 to0.32, or from 0.2 to 0.3. This allows both the devitrificationresistance and the ion exchange performance to be achieved at highlevels while the viscosity at high temperature is optimized.

A molar ratio B₂O₃/(Na₂O+Al₂O₃) is preferably from 0 to 1, from 0.01 to0.5, from 0.02 to 0.4, from 0.03 to 0.3, from 0.03 to 0.2, from 0.04 to0.18, from 0.05 to 0.17, from 0.06 to 0.16, or from 0.07 to 0.15. Thisallows both the devitrification resistance and the ion exchangeperformance to be achieved at high levels while the viscosity at hightemperature is optimized.

TiO₂ is a component that enhances the ion exchange performance of glassand is a component that reduces the viscosity at high temperature.However, when the content of TiO₂ is too large in glass, the glass isliable to be colored and to devitrify. Thus, the content of TiO₂ ispreferably from 0 to 4.5%, from 0 to 1%, from 0 to 0.5%, from 0 to 0.3%,from 0 to 0.1%, from 0 to 0.05%, or from 0 to 0.01%.

ZrO₂ is a component that enhances the ion exchange performance of glass,and is a component that increases the viscosity of glass around theliquidus viscosity and the strain point. Thus, a suitable lower limitrange of the content of ZrO₂ is 0.001% or more, 0.005% or more, 0.01% ormore, or 0.05% or more. However, when the content of ZrO₂ is excessivelyhigh, there is a risk that the devitrification resistance may lowermarkedly and the crack resistance may lower, and there is also a riskthat the density may increase excessively. Thus, a suitable upper limitrange of the content of ZrO₂ is 5% or less, 4% or less, 3% or less, 2%or less, 1% or less, 0.5% or less, 0.3% or less, or 0.1% or less.

ZnO is a component that enhances the ion exchange performance of glassand is a component that has a great effect of increasing the compressionstress value, in particular. Further, ZnO is a component that reducesthe viscosity at high temperature of glass without reducing theviscosity at low temperature. However, when the content of ZnO is toolarge in glass, there is a tendency that the glass undergoes phaseseparation, the devitrification resistance lowers, the densityincreases, and the thickness of the compression stress layer in theglass decreases. Thus, the content of ZnO is preferably from 0 to 6%,from 0 to 5%, from 0 to 3%, or from 0 to 1%.

P₂O₅ is a component that enhances the ion exchange performance of glassand is a component that increases the thickness of the compressionstress layer, in particular. However, when the content of P₂O₅ is toolarge in glass, the glass undergoes phase separation, and the waterresistance is liable to lower. Thus, the content of P₂O₅ is preferablyfrom 0 to 10%, from 0 to 3%, from 0 to 1%, from 0 to 0.5%, or from 0 to0.1%.

SnO₂ has an effect of enhancing ion exchange performance. Thus, thecontent of SnO₂ is preferably from 0 to 3%, from 0.01 to 3%, from 0.05to 3%, from 0.1 to 3%, or from 0.2 to 3%.

As a fining agent, one kind or two or more kinds selected from the groupconsisting of Cl, SO₃, and CeO₂ (preferably the group consisting of Cland SO₃) may be added at 0 to 3%.

The content of SnO₂+SO₃+Cl is preferably from 0.01 to 3%, from 0.05 to3%, from 0.1 to 3%, or from 0.2 to 3% from the viewpoint ofsimultaneously achieving a fining effect and an effect of enhancing ionexchange performance. It should be noted that the term “SnO₂+SO₃+Cl”refers to the total amount of SnO₂, Cl, and SO₃.

The content of Fe₂O₃ is preferably less than 1,000 ppm (less than 0.1%),less than 800 ppm, less than 600 ppm, less than 400 ppm, or less than300 ppm. Further, the molar ratio Fe₂O₃/(Fe₂O₃+SnO₂) is controlled topreferably 0.8 or more, 0.9 or more, or 0.95 or more, while the contentof Fe₂O₃ is controlled in the above-mentioned range. As a result, thetransmittance (400 nm to 770 nm) of glass having a thickness of 1 mm islikely to improve (by, for example, 90% or more).

A rare earth oxide such as Nb₂O₅ or La₂O₃ is a component that enhancesthe Young's modulus. However, the cost of the raw material itself ishigh, and when the rare earth oxide is added in a large amount, thedevitrification resistance is liable to deteriorate. Thus, the contentof the rare earth oxide is preferably 3% or less, 2% or less, 1% orless, 0.5% or less, or 0.1% or less.

The tempered glass of the present invention is substantially free ofAs₂O₃, Sb₂O₃, PbO, and F as a glass composition from the standpoint ofenvironmental considerations. In addition, the tempered glass ispreferably substantially free of Bi₂O₃ from the standpoint ofenvironmental considerations. The gist of the phrase “substantially freeof Bi₂O₃” resides in that Bi₂O₃ is not added positively as a glasscomponent, but contamination with Bi₂O₃ as an impurity is allowable.Specifically, the phrase means that the content of Bi₂O₃ is less than0.05%.

In the tempered glass of the present invention, the suitable contentrange of each component can be appropriately selected to attain asuitable glass composition range. Of those, particularly suitable glasscomposition ranges are as described below.

(1) A glass composition comprising, in terms of mol %, 50 to 80% ofSiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 5%of K₂O, and being substantially free of As₂O₃, Sb₂O₃, PbO, and F.

(2) A glass composition comprising, in terms of mol %, 50 to 80% ofSiO₂, 6.5 to 12.4% of Al₂O₃, 0 to 1.7% of Li₂O, more than 7.0 to 15.5%of Na₂O, 0 to 3.5% of K₂O, and 0 to 2.5% of MgO, and being substantiallyfree of As₂O₃, Sb₂O₃, PbO, and F.

(3) A glass composition comprising, in terms of mol %, 50 to 80% ofSiO₂, 6.5 to 12.4% of Al₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to3.5% of K₂O, 0.1 to 2.5% of MgO, and 0 to 2.5% of MgO+CaO+SrO+BaO, andbeing substantially free of As₂O₃, Sb₂O₃, PbO, and F.(4) A glass composition comprising, in terms of mol, 50 to 80% of SiO₂,6.5 to 12.4% of Al₂O₃, 0.01 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5%of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% ofMgO, and 0.1 to 2.5% of MgO+CaO+SrO+BaO, and being substantially free ofAs₂O₃, Sb₂O₃, PbO, and F.(5) A glass composition comprising, in terms of mol %, 50 to 77% ofSiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 13.5% ofLi₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, and being substantially free of As₂O₂,Sb₂O₃, PbO, and F.(6) A glass composition comprising, in terms of mol %, 50 to 77% ofSiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% ofLi₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratioMgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2, and beingsubstantially free of As₂O₃, Sb₂O₃, PbO, and F.(7) A glass composition comprising, in terms of mol %, 50 to 77% ofSiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O, 0 to 1% of Li₂O, 9 to15.5% of Na₂O, 0 to 3.5% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and 13 to 18.5% ofLi₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratioMgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molarratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and being substantiallyfree of As₂O₃, Sb₂O₃, PbO, and F.

The tempered glass of the present invention preferably has the followingproperties, for example.

The tempered glass of the present invention has a compression stresslayer in the surface thereof. The compression stress value of thecompression stress layer is preferably 300 MPa or more, 400 MPa or more,from 500 MPa to 1,500 MPa, or 500 MPa or more and less than 900 MPa. Asthe compression stress value becomes larger, the mechanical strength ofthe tempered glass becomes higher. It should be noted that there is atendency that the compression stress value is increased by increasingthe content of Al₂O₃, MgO, ZnO, TiO₂, or ZrO₂ in the glass compositionor by decreasing the content of SrO or BaO in the glass composition.Further, there is a tendency that the compression stress value isincreased by shortening a time necessary for ion exchange or bydecreasing the temperature of an ion exchange solution. It should benoted that when the compression stress value of the compression stresslayer is excessively large, its internal tensile stress becomesexcessively high, with the result that the tempered glass is liable toundergo spontaneous breakage.

The thickness of the compression stress layer is preferably 10 μm ormore, 15 μm or more, 15 μm or more and less than 80 μm, or 15 μm or moreand 60 μm or less. As the thickness of the compression stress layerbecomes larger, the tempered glass is more hardly cracked even when thetempered glass has a deep flaw, and a variation in the mechanicalstrength of the tempered glass becomes smaller. It should be noted thatthere is a tendency that the thickness of the compression stress layeris increased by increasing the content of K₂O or P₂O₅ in the glasscomposition or decreasing the content of SrO or BaO in the glasscomposition. In addition, there is a tendency that the thickness of thecompression stress layer is increased by lengthening an ion exchangetime or by increasing the temperature of an ion exchange solution. Itshould be noted that when the thickness of the compression stress layeris excessively large, its internal tensile stress becomes excessivelyhigh, with the result that the tempered glass is liable to undergospontaneous breakage.

The tempered glass of the present invention has a density of preferably2.6 g/cm³ or less, 2.55 g/cm³ or less, 2.50 g/cm³ ox less, 2.48 g/cm³ orless, 2.45 g/cm³ or less, 2.43 g/cm³ or less, 2.42 g/cm³ or less, 2.41g/cm³ or less, or 2.40 g/cm³ or less. As the density becomes smaller,the weight of the tempered glass can be reduced more. It should be notedthat the density is easily reduced by increasing the content of SiO₂,B₂O₃, or P₂O₅ in the glass composition or by decreasing the content ofan alkali metal oxide, alkaline earth metal oxide, ZnO, ZrO₂, or TiO₂ inthe glass composition.

The tempered glass of the present invention has a thermal expansioncoefficient in a temperature range of from 30 to 380° C. of preferably100×10⁻⁷/° C. or less, 95×10⁻⁷/° C. or less, 93×10⁻⁷/° C. or less,90×10⁻⁷/° C. or less, 88×10⁻⁷/° C. or less, 85×10⁻⁷/° C. or less,83×10⁻⁷/° C. or less, 82×10⁻⁷/° C. or less, 80×10⁻⁷/C or less, 79×10⁻⁷/°C. or less, 78×10⁻⁷/° C. or less, or from 50×10⁻⁷ to 77×10⁻⁷/° C. Whenthe thermal expansion coefficient is regulated within theabove-mentioned range, the thermal, shock resistance improves, and hencethe time required for preheating before tempering treatment or annealingafter the tempering treatment can be shortened. As a result, theproductivity of the tempered glass can be enhanced. In addition, thethermal expansion coefficient can be easily matched with that of amember such as a metal or an organic adhesive, which makes it easy toprevent the detachment of the member such as the metal or the organicadhesive. In particular, when the thermal expansion coefficient isregulated within the above-mentioned range, in the case of using thetempered glass for a tempered glass container, its breakage due to athermal shock in a heat treatment process in, for example, a glasstube-manufacturing step, processing step, or sterilizing step can beeasily prevented. It should be noted that an increase in the content ofan alkali metal oxide or alkaline earth metal oxide in the glasscomposition is likely to increase the thermal expansion coefficient, andconversely, a reduction in the content of the alkali metal oxide oralkaline earth metal oxide is likely to lower the thermal expansioncoefficient.

The tempered glass of the present invention has a temperature at10^(4.0) dPa·s of preferably 1,300° C. or less, 1,280° C. or less,1,250° C. or less, 1,220° C. or less, or 1,200° C. or less. As thetemperature at 10^(4.0) dPa·s becomes lower, a burden on a formingfacility is reduced more, the forming facility has a longer life, andconsequently, the manufacturing cost of the tempered glass is morelikely to be reduced. It should be noted that the temperature at10^(4.0) dPa·s is easily decreased by increasing the content of analkali metal oxide, an alkaline earth metal oxide, ZnO, B₂O₃, or TiO₂ orby reducing the content of SiO₂ or Al₂O₃.

The tempered glass of the present invention has a temperature at10^(2.5) dPa·s of preferably 1,650° C. or less, 1,600° C. or less,1,580° C. or less, or 1,550° C. or less. As the temperature at 10^(2.5)dPa·s becomes lower, melting at lower temperature can be carried out,and hence a burden on glass manufacturing equipment such as a meltingfurnace is reduced more, and the bubble quality of glass is improvedmore easily. That is, as the temperature at 10^(2.5) dPa·s becomeslower, the manufacturing cost of the tempered glass is more likely to bereduced. Herein, the “temperature at 10^(2.5) dPa·s” can be measured by,for example, a platinum sphere pull up method. It should be noted thatthe temperature at 10^(2.5) dPa·s corresponds to a melting temperature.In addition, an increase in the content of an alkali metal oxide,alkaline earth metal oxide, B₂O₃, ZnO, or TiO₂ in the glass compositionor a reduction in the content of SiO₂ or Al₂O₃ in the glass compositionis likely to lower the temperature at 10^(2.5) dPa·s.

The tempered glass of the present invention has a liquidus temperatureof preferably 1,200° C. or less, 1,150° C. or less, 1,100° C. or less,1,080° C. or less, 1,050° C. or less, 1,020° C. or less, or 1,000° C. orless. It should be noted that as the liquidus temperature becomes lower,the devitrification resistance and formability are improved more. Itshould be noted that the liquidus temperature is easily decreased byincreasing the content of Na₂O, K₂O, or B₂O₃ in the glass composition orby reducing the content of Al₂O₃, Li₂O, MgO, ZnO, TiO₂, or ZrO₂ in theglass composition.

The tempered glass of the present invention has a liquidus viscosity ofpreferably 10^(4.0) dPa·s or more, 10^(4.4) dPa·s or more, 10^(4.8)dPa·s or more, 10^(5.0) dPa·s or more, 10^(5.3) dPa·s or more, 10^(5.5)dPa·s or more, 10^(5.7) dPa·s or more, 10^(5.6) dPa·s or more, or10^(6.0) dPa·s or more. It should be noted that as the liquidusviscosity becomes higher, the devitrification resistance and formabilityare improved more. Further, the liquidus viscosity is easily increasedby increasing the content of Na₂O or K₂O in the glass composition or byreducing the content of Al₂O₃, Li₂O, MgO, ZnO, TiO₂, or ZrO₂ in theglass composition.

The tempered glass of the present invention has a crack resistancebefore tempering treatment of preferably 100 gf or more, 200 gf or more,300 gf or more, 400 gf or more, 500 gf or more, 600 gf or more, 700 gfor more, 800 gf or more, 900 gf or more, or 1,000 gf or more. As thecrack resistance increases, a surface flaw is less liable to be createdon the tempered glass, and hence the mechanical strength of the temperedglass is less liable to lower. In addition, the mechanical strength isless liable to vary. In addition, when the crack resistance is high, alateral crack is hardly generated at the time of post-tempering cuttingsuch as scribe cutting, and hence the post-tempering scribe cutting canbe easily performed appropriately. As a result, the manufacturing costof a device can be easily reduced.

Herein, the “crack resistance” refers to a load at a crack generationrate of 50%. In addition, the “crack generation rate” refers to a valuemeasured as described below. First, in a constant temperature andhumidity chamber kept at a humidity of 30% and a temperature of 25° C.,a Vickers indenter set to a predetermined load is driven into a glasssurface (optically polished surface) for 1.5 seconds, and 15 secondsafter that, the number of cracks generated from the four corners of theindentation is counted (4 per indentation at maximum). The indenter isdriven in this manner 20 times, the total number of generated cracks isdetermined, and then the crack generation rate is determined by thefollowing expression: total number of generated cracks/80×100.

When the tempered glass of the present invention is immersed in a 10mass % aqueous hydrochloric acid solution at 80° C. for 24 hours, itsmass reduction is preferably 150 mg/cm² or less, 100 mg/cm² or less, 50mg/cm² or less, 45 mg/cm² or less, 40 mg/cm² or less, 30 mg/cm² or less,20 mg/cm² or less, 10 mg/cm² or less, 5 mg/cm² or less, 3 mg/cm² orless, 1 mg/cm² or less, 0.8 mg/cm² or less, 0.7 mg/cm² or less, 0.6mg/cm² or less, 0.5 mg/cm² or less, 0.4 mg/cm² or less, 0.3 mg/cm² orless, 0.2 mg/cm² or less, or 0.1 mg/cm² or less. As the mass reductionreduces, the tempered glass becomes less liable to be corroded by achemical. Thus, the tempered glass can be appropriately treated in aphotoresist step or the like.

A tempered glass sheet of the present invention comprises the temperedglass described above. Thus, technical features (suitablecharacteristics, suitable component ranges, and the like) of thetempered glass sheet of the present invention are the same as thetechnical features of the tempered glass of the present invention inprinciple, and hence detailed descriptions of the technical features ofthe tempered glass sheet of the present invention are omitted here.

The surface of the tempered glass sheet of the present invention has anaverage surface roughness (Ra) of preferably 10 Å or less, 8 Å or less,6 Å or less, 4 Å or less, 3 Å or less, particularly 2 Å or less. As theaverage surface roughness (Ra) increases, the mechanical strength of thetempered glass sheet tends to become lower. Herein, the average surfaceroughness (Ra) refers to a value measured by a method in conformity withSEMI D7-97 “FPD Glass Substrate Surface Roughness Measurement Method.”

The tempered glass sheet of the present invention has a length dimensionof preferably 500 mm or more, 700 mm or more, or 1,000 mm or more and awidth dimension of preferably 500 mm or more, 700 mm or more, or 1,000mm or more. An increase in the size of the tempered glass sheet enablesthe tempered glass sheet to be suitably used as a cover glass for thedisplay portion of the display of a large-size TV or the like.

The sheet thickness of the tempered glass sheet of the present inventionis preferably 2.0 mm or less, 1.5 mm or less, 1.3 mm or less, 1.1 mm orless, 1.0 mm or less, 0.8 mm or less, or 0.7 mm or less. Meanwhile, whenthe sheet thickness is excessively small, desired mechanical strength isdifficult to obtain. Thus, the sheet thickness is preferably 0.1 mm ormore.

In the tempered glass sheet of the present invention, it is preferred toattach a protective resin film onto at least one surface of the temperedglass sheet, and it is more preferred to attach the protective resinfilm onto each of both surfaces of the tempered glass sheet. A materialfor the protective resin film is preferably capable of being detachablyattached onto the surface of the tempered glass sheet. With this, asituation in which a flaw is created in the surface of the temperedglass sheet during the transportation or shipment of the tempered glasssheet to lower the mechanical strength of the tempered glass sheet canbe easily prevented. Further, in the case of, for example, forming afunctional film such as a transparent conductive film on the surface ofthe tempered glass sheet, the protective resin film can be easily peeledfrom the surface of the tempered glass sheet. From the viewpoint ofattachment efficiency, the size (longitudinal dimension×lateraldimension) of the protective resin film is preferably smaller than thesize of the tempered glass sheet. From the viewpoint of preventing thetempered glass sheet from having a surface flaw, at least one of thelongitudinal dimension and lateral dimension of the protective resinfilm is preferably set equal to or larger than that of the temperedglass sheet, and the surface of the tempered glass sheet is morepreferably covered completely with the protective resin film. It shouldbe noted that the thickness of the protective resin film is preferablysmaller than the sheet thickness of the tempered glass sheet from theviewpoint of a packaging ratio or the like.

A tempered glass container of the present invention comprises thetempered glass described above. Thus, technical features (suitablecharacteristics, suitable component ranges, and the like) of thetempered glass container of the present invention are the same as thetechnical features of the tempered glass of the present invention inprinciple. Detailed descriptions of the technical features of thetempered glass container of the present invention are omitted here.

The tempered glass container of the present invention is preferablyobtained by processing a glass tube into a glass container and thensubjecting the glass container to tempering treatment. The glass tubepreferably has an outer diameter dimension of from 5 to 50 mm, from 5 to40 mm, or from 5 to 30 mm, and preferably has a thickness dimension offrom 0.3 to 2 mm, from 0.3 to 1.5 mm, or from 0.4 to 1.5 mm.

A glass to be tempered of the present invention is a glass to besubjected to tempering treatment, comprising as a glass composition, interms of mol %, 50 to 80% of SiO₂, 5 to 30% of Al₂O₃, 0 to 2% of Li₂O, 5to 25% of Na₂O, and 0 to 5% of K₂O, and being substantially free ofAs₂O₃, Sb₂O₃, PbO, and F. Thus, technical features (suitablecharacteristics, suitable component ranges, and the like) of the glassto be tempered of the present invention are the same as the technicalfeatures of the tempered glass of the present invention and the temperedglass sheet of the present invention in principle, and hence detaileddescriptions of the technical features of the glass to be tempered ofthe present invention are omitted here.

The glass to be tempered of the present invention has a crack resistanceof preferably 100 gf or more, 200 gf or more, 300 gf or more, 400 gf ormore, 500 gf or more, 600 gf or more, 700 gf or more, 800 gf or more,900 gf or more, or 1,000 gf or more. As the crack resistance increases,a surface flaw is less liable to be created on a tempered glass to beobtained, and hence the mechanical strength of the tempered glass isless liable to lower. In addition, the mechanical strength is lessliable to vary. In addition, when the crack resistance is high, alateral crack is hardly generated at the time of post-tempering cuttingsuch as scribe cutting, and hence the post-tempering scribe cutting canbe easily performed appropriately. As a result, the manufacturing costof a device can be easily reduced.

In a glass sheet to be tempered of the present invention, it ispreferred to attach a protective resin film onto at least one surface ofthe glass sheet to be tempered, and it is more preferred to attach theprotective resin film onto each of both surfaces of the glass sheet tobe tempered. A material for the protective resin film is preferablycapable of being detachably attached onto the surface of the glass sheetto be tempered. With this, a situation in which a flaw is created in thesurface of the glass sheet to be tempered during the transportation orshipment of the glass sheet to be tempered to lower the mechanicalstrength of the tempered glass sheet can be easily prevented. Further,in the case of, for example, subjecting the glass sheet to be temperedto ion exchange treatment, the protective resin film can be easilypeeled from the surface of the glass sheet to be tempered. From theviewpoint of attachment efficiency, the size (longitudinaldimension×lateral dimension) of the protective resin film is preferablysmaller than the size of the glass sheet to be tempered. From theviewpoint of preventing the glass sheet to be tempered from having asurface flaw, at least one of the longitudinal dimension and lateraldimension of the protective resin film is preferably set equal to orlarger than that of the glass sheet to be tempered, and the surface ofthe glass sheet to be tempered is more preferably covered completelywith the protective resin film. It should be noted that the thickness ofthe protective resin film is preferably smaller than the sheet thicknessof the glass sheet to be tempered from the viewpoint of a packagingratio or the like.

Specific examples of the case where the protective resin film isattached onto the glass sheet to be tempered are described below. Asillustrated in FIG. 1a , in such a manner that a protective resin film 1having a rectangular shape is protruded beyond two parallel sides of aglass sheet to be tempered 2 having a rectangular shape and a protrudingdimension a beyond each of the two sides is set to about 10 nm, theprotective resin film 1 may be attached onto one surface, or each ofboth surfaces, of the glass sheet to be tempered 2. In addition, asillustrated in FIG. 1b , in such a manner that the protective resin film1 having a rectangular shape is protruded beyond only one side of theglass sheet to be tempered 2 having a rectangular shape and a protrudingdimension b beyond the side is set to about 10 mm, the protective resinfilm 1 may be attached onto one surface, or each of both surfaces, ofthe glass sheet to be tempered 2. Further, as illustrated in FIG. 1c ,in such a manner that the four sides of the glass sheet to be tempered 2having a rectangular shape are protruded beyond the protective resinfilm 1 having a rectangular shape, the protective resin film 1 may beattached onto one surface, or each of both surfaces, of the glass sheetto be tempered 2. In addition, as illustrated in FIG. 1d , in such amanner that the protective resin film 1 having a rectangular shape isprotruded beyond the four sides of the glass sheet to be tempered 2having a rectangular shape, the protective resin film 1 may be attachedonto one surface, or each of both surfaces, of the glass sheet to betempered 2. It should be noted that the attachment states of theprotective resin film 1 with respect to the glass sheet to be tempered 2as described above may be similarly applied to the attachment state ofthe protective resin film with respect to the above-mentioned temperedglass sheet.

When the glass to be tempered of the present invention is subjected toion exchange treatment in a KNO₃ molten salt (having no history of beingused) at 430° C., it is preferred that the compression stress value of acompression stress layer in a surface thereof be 300 MPa or more and thethickness of the compression stress layer be 10 μm or more, it is morepreferred that the compression stress of the surface thereof be 400 MPaor more and the thickness of the compression stress layer be 15 μm ormore, and it is particularly preferred that the compression stress ofthe surface thereof be 500 MPa or more and the thickness of thecompression stress layer be 15 μm or more.

The glass to be tempered of the present invention preferably has a ratioCS₂/CS₁ of a compression stress value CS₂ to a compression stress valueCS) of 0.7 or more, 0.71 or more, 0.72 or more, or 0.73 or more, thecompression stress value CS₁ being determined for a compression stresslayer that is obtained by subjecting the glass to be tempered to ionexchange treatment in a potassium nitrate molten salt free of a historyof being used, the compression stress value CS₂ being determined for acompression stress layer that is obtained by subjecting the glass to betempered to ion exchange treatment in a potassium nitrate molten saltcomprising 20,000 ppm (by mass) of Na ions. With this, even when adeteriorated ion exchange solution is used, the ion exchange performancecan be easily maintained. As a result, the replacement interval of theion exchange solution can be lengthened.

When the ion exchange treatment is performed, the temperature of theKNO₃ molten salt is preferably from 400 to 550° C., and the ion exchangetime is preferably from 0.5 to 10 hours, particularly preferably from0.5 to 4 hours. Under the conditions, the compression stress layer canbe properly formed easily. It should be noted that the glass to betempered of the present invention has the above-mentioned glasscomposition, and hence the compression stress value and thickness of thecompression stress layer can be increased without using a mixture of aKNO₃ molten salt and a NaNO₃ molten salt or the like.

The glass to be tempered, tempered glass, tempered glass container, andtempered glass sheet of the present invention can be produced asdescribed below.

First, glass raw materials, which have been blended so as to have theabove-mentioned glass composition, are loaded in a continuous meltingfurnace, are melted by heating at 1,500 to 1,650° C., and are fined.After that, the resultant is fed to a forming apparatus, is formed into,for example, a sheet shape or a tube shape, and is annealed. Thus, aglass sheet, a glass tube, or the like can be produced.

An overflow down-draw method is preferably adopted as a method offorming the glass sheet. The overflow down-draw method is a method bywhich a high-quality glass sheet can be produced in a large amount, andby which even a large-size glass sheet can be easily produced. Inaddition, the method allows flaws on the surface of the glass sheet tobe reduced to the extent possible.

Various forming methods other than the overflow down-draw method mayalso be adopted. For example, forming methods such as a float method, adown draw method (such as a slot down method or a re-draw method), aroll out method, and a press method may be adopted.

In addition, as a method of forming a glass tube, it is preferred toadopt a down-draw method, an up-draw method, a Vello method, or a Dannermethod. Particularly from the viewpoint of production efficiency, theDanner method is preferably adopted. In this context, the Danner methodis a method comprising winding molten glass on the surface of a rotatingcylindrical refractory, allowing the glass to flow down to the end ofthe refractory, and drawing the glass out of the end of the refractoryinto a tube shape while blowing air into the glass. After that, theglass tube can be processed into the glass container through localheating with a gas burner. It should be noted that residual straingenerated at the time of the processing can be removed by putting theglass tube into an annealing furnace.

Next, the resultant glass to be tempered is subjected to temperingtreatment, thereby being able to produce a tempered glass. The resultanttempered glass may be cut into pieces having predetermined sizes beforethe tempering treatment, but the cutting is preferably performed afterthe tempering treatment from the viewpoint of the manufacturingefficiency of a device.

The tempering treatment is preferably ion exchange treatment. Conditionsfor the ion exchange treatment are not particularly limited, and optimumconditions may be selected in view of, for example, the viscosityproperties, applications, thickness, inner tensile stress, anddimensional change of glass. The ion exchange treatment can beperformed, for example, by immersing the glass to be tempered in a KNO₃molten salt at 400 to 550° C. for 0.5 to 10 hours. Particularly when theion exchange of K ions in the KNO₃ molten salt with Na components in theglass is performed, it is possible to form efficiently a compressionstress layer in a surface of the glass.

It is preferred that an end surface of the glass sheet to be tempered besubjected to etching treatment and then the glass sheet to be temperedbe subjected to ion exchange treatment to provide the tempered glasssheet. With this, the end surface is brought into a smooth state, and acompression stress layer is formed in such end surface. Accordingly, themechanical strength, in particular, three-point bending strength, of thetempered glass sheet can be significantly enhanced. An etching liquid tobe used in the etching treatment is preferably a solution comprising F,particularly preferably an aqueous solution comprising HF. With this,the end surface can be easily etched so as to be brought into a smoothstate.

It is also preferred that an end surface of the glass sheet to betempered be fire-polished and then the glass sheet to be tempered besubjected to ion exchange treatment to provide the tempered glass sheet.With this, the end surface is brought into a smooth state, and acompression stress layer is formed in such end surface. Accordingly, themechanical strength, in particular, three-point bending strength, of thetempered glass sheet can be significantly enhanced.

It is also preferred that an end surface of the glass sheet to betempered be subjected to polishing processing, in particular, chamferingprocessing and then the glass sheet to be tempered be subjected to ionexchange treatment to provide the tempered glass sheet. With this, theend surface is brought into a smooth state, and a compression stresslayer is formed in such end surface. Accordingly, the mechanical,strength, in particular, three-point bending strength, of the temperedglass sheet can be significantly enhanced.

When the tempered glass sheet is cut, laser cutting or scribe cutting ispreferably adopted. A CO₂ laser or a short-pulse laser is preferablyused in the laser cutting. With this, an unintended crack is hardlydeveloped at the time of the cutting.

When the tempered glass sheet is subjected to the scribe cutting, it ispreferred that the depth of an initial cut (scribing cut) be larger thanthe thickness of the compression stress layer and the tempered glasssheet have an internal tensile stress of 100 MPa or less, 80 MPa orless, 70 MPa or less, 60 MPa or less, 40 MPa or less, 30 MPa or less, 25MPa or less, 23 MPa or less, or 20 MPa or less. In addition, scribing ispreferably started from one end of the tempered glass sheet or from aregion at a distance of 5 mm or more therefrom, and the scribing ispreferably stopped at a region at a distance of 5 mm or more from theother end of the tempered glass sheet. Further, a snapping step ispreferably provided after the scribing. With this, an unintended crackis hardly generated at the time of the scribing, and hence thepost-tempering scribe cutting can be easily performed appropriately. Itshould be noted that the internal tensile stress can be calculated bythe following equation 1. For example, a wheel cutter having aprotrusion on its outer circumference is preferably used for forming thescribing cut.Internal tensile stress=(compression stress value of compression stresslayer×thickness of compression stress layer)/{sheetthickness−2×(thickness of compression stress layer)}  <Equation 1>

It is preferred that after the glass sheet to be tempered has beensubjected to ion exchange treatment to provide the tempered glass sheet,an end surface of the tempered glass sheet be subjected to etchingtreatment, and it is more preferred that after the glass sheet to betempered has been subjected to ion exchange treatment to provide thetempered glass sheet, an end surface of the tempered glass sheet besubjected to polishing processing, in particular, chamfering process ingand then the end surface be subjected to etching treatment. With this,the end surface is brought into a smooth state, and hence even when theend surface has no compression stress layer formed therein, themechanical strength, in particular, three-point bending strength, of thetempered glass sheet can be enhanced. An etching liquid to be used inthe etching treatment is preferably a solution comprising F,particularly preferably an aqueous solution comprising HF. With this,the end surface can be easily etched so as to be brought into a smoothstate.

EXAMPLES

The present invention is hereinafter described based on Examples. Itshould be noted that the following examples are merely illustrative. Thepresent invention is by no means limited to these examples.

Tables 1 to 8 show examples of the present invention (sample Nos. 1 to45).

TABLE 1 Example No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Glass SiO₂ 68.2 67.467.2 66.4 68.8 68.0 com- Al₂O₃ 11.6 12.2 11.6 12.3 11.6 12.3 positionMgO 2.5 2.5 2.5 2.5 0.8 0.8 (mol %) B₂O₃ 4.9 5.1 6.0 6.0 5.2 5.2 Na₂O11.3 11.4 11.3 11.4 12.4 12.5 K₂O 1.4 1.4 1.4 1.4 1.1 1.1 SnO₂ 0.1 0.10.1 0.1 0.1 0.1 Li₂O + Na₂O + 12.7 12.8 12.7 12.8 13.5 13.6 K₂O MgO +CaO + 2.48 2.47 2.48 2.50 0.78 0.81 SrO + BaO Li₂O + Na₂O + 15.20 15.2415.19 15.26 14.29 14.39 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O + 0.160.16 0.16 0.16 0.05 0.06 Na₂O + K₂O + MgO + CaO + SrO + BaO) (Al₂O₃ +B₂O₃)/ 0.24 0.26 0.26 0.28 0.24 0.26 SiO₂ Density (g/cm³) 2.39 2.39 2.382.38 2.39 2.39 α (×10⁻⁷/° C.) 74 75 75 75 77 78 Ps (° C.) 563 569 556561 557 561 Ta (° C.) 615 624 607 614 607 614 Ts (° C.) 885 899 881 884862 892 10⁴ dPa · s 1,323 1,330 1,305 1,322 1,323 1,343 (° C.) 10³ dPa ·s 1,537 1,538 1,518 1,526 1,550 1,561 (° C.) 10^(2.5) dP · s 1,670 1,6711,649 1,652 1,692 1,695 (° C.) TL (° C.)1,139 >1,160 >1,160 >1,160 >1,160 1,160 LogηTL 5.1 <5.1 <4.9 <5.0 <4.95.1 (dPa · s) Chemical 0.3 0.7 0.7 1.4 0.3 0.5 resistance [10 mass %hydrochloric acid at 80° C. for 24 h] Mass reduction (mg/cm²) CS₁ (MPa)838 867 826 845 871 906 DOL₁ (μm) 37 39 35 36 38 40 CS₂ (MPa) 598 624610 620 647 670 DOL₂ (μm) 35 36 34 34 35 38 CS₂/CS₁ 0.71 0.72 0.74 0.730.74 0.74

TABLE 2 Example No. 7 No. 8 No. 9 No. 10 No. 11 No. 12 Glass SiO₂ 67.867.2 68.0 69.6 68.7 67.6 com- Al₂O₃ 11.6 12.3 11.5 10.8 10.8 10.8position MgO 0.8 0.8 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 6.1 6.0 3.4 2.6 3.64.7 Na₂O 12.4 12.5 15.4 15.3 15.3 15.2 K₂O 1.1 1.1 0.0 0.0 0.0 0.0 SnO₂0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 13.5 13.6 15.4 15.3 15.3 15.2 K₂OMgO + CaO + 0.80 0.81 1.60 1.60 1.60 1.59 SrO + BaO Li₂O + Na₂O + 14.3414.41 17.00 16.90 16.87 16.77 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O +0.06 0.06 0.09 0.09 0.09 0.09 Na₂O + K₂O + MgO + CaO + SrO + BaO)(Al₂O₃ + B₂O₃)/ 0.26 0.27 0.22 0.19 0.21 0.23 SiO₂ Density (g/cm³) 2.392.38 2.42 2.42 2.42 2.42 α (×10⁻⁷/° C.) 77 78 81 81 80 80 Ps (° C.) 551556 560 562 557 553 Ta (° C.) 601 608 606 608 601 596 Ts (° C.) 856 873835 840 824 810   10⁴ dPa · s 1,302 1,326 1,263 1,266 1,249 1,227 (° C.)  10³ dPa · s 1,529 1,545 1,487 1,499 1,478 1,454 (° C.) 10^(2.5) dPa ·s 1,667 1,680 1,624 1,646 1,622 1,597 (° C.) TL (° C.) 1,032 1,141 981979 963 940 LogηTL 5.8 5.1 5.9 6.0 6.0 6.0 (dPa · s) Chemical 0.5 0.90.3 0.1 0.1 0.2 resistance [10 mass % hydrochloric acid at 80° C. for 24h] Mass reduction (mg/cm²) CS₁ (MPa) 855 887 909 821 846 853 DOL₁ (μm)36 38 32 31 29 27 CS₂ (MPa) 639 661 695 652 645 664 DOL₂ (μm) 33 35 3029 27 25 CS₂/CS₁ 0.75 0.74 0.76 0.79 0.76 0.78

TABLE 3 Example No. 13 No. 14 No. 15 No. 16 No. 17 No. 18 Glass SiO₂68.1 67.1 69.9 68.8 68.9 68.0 com- Al₂O₃ 11.5 11.6 10.9 10.8 11.5 11.5position MgO 1.6 1.6 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 3.6 4.5 2.5 3.6 3.64.4 Na₂O 14.4 14.4 14.3 14.3 14.3 14.3 K₂O 0.7 0.7 0.7 0.7 0.0 0.0 SnO₂0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 15.1 15.1 15.0 15.0 14.3 14.4 K₂OMgO + CaO + 1.62 1.64 1.61 1.64 1.61 1.63 SrO + BaO Li₂O + Na₂O + 16.7216.74 16.63 16.66 15.95 16.00 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O +0.10 0.10 0.10 0.10 0.10 0.10 Na₂O + K₂O + MgO + CaO + SrO + BaO)(Al₂O₃ + B₂O₃)/ 0.22 0.24 0.19 0.21 0.22 0.23 SiO₂ Density (g/cm³) 2.422.42 2.42 2.42 2.41 2.41 α (×10⁻⁷/° C.) 82 82 81 81 77 77 Ps (° C.) 558554 561 556 568 561 Ta (° C.) 605 599 607 600 617 608 Ts (° C.) 840 826843 827 864 846   10⁴ dPa · s 1,275 1,250 1,278 1,255 1,296 1,281 (° C.)  10³ dPa · s 1,503 1,474 1,506 1,486 1,519 1,504 (° C.) 10^(2.5) dPa ·s 1,641 1,613 1,645 1,632 1,653 1,640 (° C.) TL (° C.) 940 953 1,0011,006 960 973 LogηTL 6.4 6.1 5.9 5.6 6.5 6.2 (dPa · s) Chemical 0.3 0.60.1 0.5 0.1 0.3 resistance [10 mass % hydrochloric acid at 80° C. for 24h] Mass reduction (mg/cm²) CS₁ (MPa) 860 863 816 828 860 831 DOL₁ (μm)33 31 34 32 31 32 CS₂ (MPa) 651 655 623 624 673 662 DOL₂ (μm) 31 29 3229 28 26 CS₂/CS₁ 0.76 0.76 0.76 0.75 0.78 0.80

TABLE 4 Example No. 19 No. 20 No. 21 No. 22 No. 23 No. 24 Glass SiO₂70.4 69.7 68.5 68.1 67.8 67.6 com- Al₂O₃ 10.7 10.8 11.4 11.4 11.5 11.4position MgO 1.6 1.6 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 2.8 3.6 3.7 3.8 3.73.7 Na₂O 14.3 14.2 13.9 13.9 13.9 14.5 K₂O 0.0 0.0 0.7 1.0 1.4 1.0 SnO₂0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 14.3 14.3 14.6 15.0 15.3 15.5 K₂OMgO + CaO + 1.60 1.61 1.61 1.60 1.61 1.62 SrO + BaO Li₂O + Na₂O + 15.9315.86 16.26 16.59 16.92 17.13 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O +0.10 0.10 0.10 0.10 0.09 0.09 Na₂O + K₂O + MgO + CaO + SrO + BaO)(Al₂O₃ + B₂O₃)/ 0.19 0.21 0.22 0.22 0.22 0.22 SiO₂ Density (g/cm³) 2.412.41 2.41 2.42 2.42 2.42 α (×10⁻⁷/° C.) 77 77 81 82 84 84 Ps (° C.) 570564 564 560 554 556 Ta (° C.) 619 610 612 607 600 602 Ts (° C.) 865 847856 846 836 830   10⁴ dPa · s 1,301 1,292 1,297 1,284 1,263 1,269 (° C.)  10³ dPa · s 1,530 1,520 1,522 1,511 1,491 1,495 (° C.) 10^(2.5) dPa ·s 1,673 1,658 1,657 1,656 1,630 1,636 (° C.) TL (° C.) 1,021 1,034 974964 957 967 LogηTL 5.9 5.6 6.3 6.2 6.2 6.1 (dPa · s) Chemical 0.3 0.10.2 0.2 0.3 0.4 resistance [10 mass % hydrochloric acid at 80° C. for 24h] Mass reduction (mg/cm²) CS₁ (MPa) 830 845 903 893 873 882 DOL₁ (μm)32 30 34 35 37 35 CS₂ (MPa) 645 649 674 656 639 651 DOL₂ (μm) 30 27 3233 35 33 CS₂/CS₁ 0.78 0.77 0.75 0.75 0.73 0.74

TABLE 5 Example No. 25 No. 26 No. 27 No. 28 No. 29 No. 30 Glass SiO₂67.4 67.5 66.6 66.8 66.3 67.4 com- Al₂O₃ 11.7 11.7 11.6 11.8 11.6 10.9position MgO 1.6 1.6 1.6 1.6 0.8 0.8 (mol %) B₂O₃ 3.5 3.2 3.5 3.1 6.36.3 Na₂O 14.4 15.2 15.4 15.2 13.8 13.4 K₂O 1.3 0.7 1.0 1.3 1.1 1.0 SnO₂0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 15.7 15.9 16.5 16.5 14.9 14.5 K₂OMgO + CaO + 1.64 1.64 1.64 1.66 0.82 0.81 SrO + BaO Li₂O + Na₂O + 17.3517.59 18.11 18.19 15.73 15.28 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O +0.09 0.09 0.09 0.09 0.05 0.05 Na₂O + K₂O + MgO + CaO + SrO + BaO)(Al₂O₃ + B₂O₃)/ 0.23 0.22 0.23 0.22 0.27 0.25 SiO₂ Density (g/cm³) 2.432.43 2.44 2.44 2.40 2.41 α (×10⁻⁷/° C.) 85 85 86 88 82 79 Ps (° C.) 552552 549 550 542 545 Ta (° C.) 597 596 592 593 586 588 Ts (° C.) 826 817808 815 805 803   10⁴ dPa · s 1,282 1,273 1,233 1,257 1,223 1,229 (° C.)  10³ dPa · s 1,504 1,494 1,459 1,479 1,458 1,466 (° C.) 10^(2.5) dPa ·s 1,645 1,633 1,599 1,616 1,607 1,622 (° C.) TL (° C.) 908 923 909 893977 986 LogηTL 6.6 6.4 6.4 6.7 5.6 5.6 (dPa · s) Chemical 0.6 0.6 0.70.7 1.0 0.5 resistance [10 mass % hydrochloric acid at 80° C. for 24 h]Mass reduction (mg/cm²) CS₁ (MPa) 871 879 849 855 871 858 DOL₁ (μm) 3633 35 36 32 31 CS₂ (MPa) 645 659 636 634 653 632 DOL₂ (μm) 35 32 32 3530 30 CS₂/CS₁ 0.74 0.75 0.75 0.74 0.75 0.74

TABLE 6 Example No. 31 No. 32 No. 33 No. 34 No. 35 No. 36 Glass SiO₂68.3 65.9 66.7 67.3 64.8 65.6 com- Al₂O₃ 10.3 11.6 11.0 10.3 11.6 11.0position MgO 0.8 0.8 0.8 0.8 0.8 0.8 (mol %) B₂O₃ 6.1 7.1 7.0 7.2 8.18.0 Na₂O 13.4 13.5 13.3 13.3 13.5 13.5 K₂O 1.0 1.0 1.0 1.0 1.0 1.0 SnO₂0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 14.4 14.5 14.4 14.3 14.5 14.5 K₂OMgO + CaO + 0.79 0.82 0.82 0.81 0.82 0.82 SrO + BaO Li₂O + Na₂O + 15.2115.36 15.20 15.13 15.35 15.31 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O +0.05 0.05 0.05 0.05 0.05 0.05 Na₂O + K₂O + MgO + CaO + SrO + BaO)(Al₂O₃ + B₂O₃)/ 0.24 0.28 0.27 0.26 0.30 0.29 SiO₂ Density (g/cm³) 2.412.40 2.40 2.40 2.39 2.40 α (×10⁻⁷/° C.) 79 80 80 79 80 80 Ps (° C.) 546541 540 540 535 535 Ta (° C.) 589 585 583 582 578 577 Ts (° C.) 799 804793 786 793 783   10⁴ dPa · s 1,206 1,226 1,214 1,190 1,224 1,194 (° C.)  10³ dPa · s 1,446 1,457 1,453 1,427 1,450 1,430 (° C.) 10^(2.5) dPa ·s 1,595 1,603 1,601 1,578 1,586 1,578 (° C.) TL (° C.) 967 985 984 942992 943 LogηTL 5.6 5.6 5.5 5.7 5.5 5.7 (dPa · s) Chemical 0.2 1.3 0.80.4 15.3 1.2 resistance [10 mass % hydrochloric acid at 80° C. for 24 h]Mass reduction (mg/cm²) CS₁ (MPa) 830 870 843 823 850 824 DOL₁ (μm) 3031 31 28 30 29 CS₂ (MPa) 615 651 637 619 642 631 DOL₂ (μm) 28 30 28 2728 28 CS₂/CS₁ 0.74 0.75 0.75 0.75 0.75 0.77

TABLE 7 Example No. 37 No. 38 No. 39 No. 40 No. 41 No. 42 Glass SiO₂66.6 68.8 69.4 67.1 67.9 69.0 com- Al₂O₃ 10.3 10.8 10.2 11.5 10.9 10.2position MgO 0.8 1.6 1.6 1.6 1.6 1.6 (mol %) B₂O₃ 7.8 3.6 3.7 4.6 4.54.4 Na₂O 13.3 14.3 14.3 14.4 14.2 14.0 K₂O 1.0 0.7 0.7 0.7 0.7 0.6 SnO₂0.1 0.1 0.1 0.1 0.1 0.1 Li₂O + Na₂O + 14.3 15.0 15.0 15.1 14.9 14.7 K₂OMgO + CaO + 0.82 1.64 1.62 1.65 1.65 1.65 SrO + BaO Li₂O + Na₂O + 15.1116.68 16.60 16.77 16.56 16.31 K₂O + MgO + CaO + SrO + BaO MgO/(Li₂O +0.05 0.10 0.10 0.10 0.10 0.10 Na₂O + K₂O + MgO + CaO + SrO + BaO)(Al₂O₃ + B₂O₃)/ 0.27 0.21 0.20 0.24 0.23 0.21 SiO₂ Density (g/cm³) 2.402.42 2.42 2.42 2.42 2.42 α (×10⁻⁷/° C.) 79 82 81 81 81 80 Ps (° C.) 536557 556 552 553 533 Ta (° C.) 578 602 600 596 597 596 Ts (° C.) 779 830825 822 818 812   10⁴ dPa · s 1,168 1,281 1,254 1,250 1,267 1,284 (° C.)  10³ dPa · s 1,402 1,511 1,485 1,475 1,494 1,515 (° C.) 10^(2.5) dPa ·s 1,554 1,656 1,629 1,615 1,636 1,662 (° C.) TL (° C.) 930 928 947 956930 949 LogηTL 5.7 6.5 6.2 6.0 6.3 6.1 (dPa · s) Chemical 0.9 0.1 0.10.5 0.2 0.1 resistance [10 mass % hydrochloric acid at 80° C. for 24 h]Mass reduction (mg/cm²) CS₁ (MPa) 812 876 850 909 886 856 DOL₁ (μm) 2732 32 32 30 30 CS₂ (MPa) 616 652 622 672 652 642 DOL₂ (μm) 25 30 29 2929 27 CS₂/CS₁ 0.76 0.74 0.73 0.74 0.74 0.75

TABLE 8 Example No. 43 No. 44 No. 45 Glass SiO₂ 66.0 66.9 67.7composition Al₂O₃ 11.5 10.9 10.2 (mol %) MgO 1.6 1.6 1.6 B₂O₃ 5.7 5.65.5 Na₂O 14.4 14.2 14.1 K₂O 0.7 0.7 0.6 SnO₂ 0.1 0.1 0.1 Li₂O + Na₂O +K₂O 15.1 14.9 14.8 MgO + CaO + SrO + BaO 1.65 1.66 1.65 Li₂O + Na₂O +K₂O + MgO + 16.72 16.54 16.44 CaO + SrO + BaO MgO/(Li₂O + Na₂O + K₂O +0.10 0.10 0.10 MgO + CaO + SrO + BaO) (Al₂O₃ + B₂O₃)/SiO₂ 0.26 0.25 0.23Density (g/cm³) 2.42 2.42 2.42 α (×10⁻⁷/° C.) 82 80 80 Ps (° C.) 549 547546 Ta (° C.) 592 590 588 Ts (° C.) 811 809 796 10⁴ dPa · s (° C.) 1,2391,239 1,250 10³ dPa · s (° C.) 1,464 1,467 1,478 10^(2.5) dPa · s (° C.)1,600 1,608 1,624 TL (° C.) 944 959 966 logηTL (dPa · s) 6.0 5.9 5.8Chemical resistance 0.8 0.5 0.2 [10 mass % hydrochloric acid at 80° C.for 24 h] Mass reduction (mg/cm²) CS₁ (MPa) 903 898 844 DOL₁ (μm) 30 3028 CS₂ (MPa) 671 655 629 DOL₂ (μm) 27 27 26 CS₂/CS₁ 0.74 0.73 0.75

Each of the samples in the tables was produced as described below.First, glass raw materials were blended so as to have glass compositionsshown in the tables, and melted at 1,600° C. using a platinum pot. Thetime period of the melting was set to 21 hours. Thereafter, theresultant molten glass was cast on a carbon plate and formed into asheet shape. The resultant glass sheet was evaluated for its variousproperties.

The density is a value obtained through measurement by a knownArchimedes method.

The thermal expansion coefficient α is a value obtained throughmeasurement of an average thermal expansion coefficient in a temperaturerange of from 30 to 380° C. using a dilatometer.

The strain point Ps and the annealing point Ta are values obtainedthrough measurement based on a method of ASTM C336.

The softening point Ts is a value obtained through measurement based ona method of ASTM C338.

The temperatures at the viscosities at high temperature of 10^(4.0)dPa·s, 10^(3.0) dPa·s, and 10^(2.5) dPa·s are values obtained throughmeasurement by a platinum sphere pull up method.

The liquidus temperature TL is a value obtained through measurement of atemperature at which crystals of glass are deposited after glass powderthat passes through a standard 30-mesh sieve (sieve opening: 500 μm) andremains on a 50-mesh sieve (sieve opening: 300 μm) is placed in aplatinum boat and then kept for 24 hours in a gradient heating furnace.

The liquidus viscosity log η_(n), is a value obtained throughmeasurement of a viscosity of glass at the liquidus temperature by aplatinum sphere pull up method.

The chemical resistance is a mass reduction after immersion in a 10 mass% aqueous hydrochloric acid solution at 80° C. for 24 hours. The massreduction of each sample was measured as described below. First, themass and surface area of each sample before its immersion in the aqueoushydrochloric acid solution were measured. Next, each sample was immersedin the aqueous hydrochloric acid solution, and then the mass of eachsample was measured. Finally, the mass reduction was calculated by thefollowing expression: (mass before immersion-mass afterimmersion)/(surface area before immersion).

As evident from Tables 1 to 8, each of the samples had a density of 2.44q/cm³ or less and a thermal expansion coefficient of 88×10⁻⁷/° C. orless. Further, each of the samples has a liquidus viscosity of 10^(4.0)dPa·s or more, thus being able to be formed into a sheet shape by theoverflow down-draw method, and moreover, has a temperature at 10^(2.5)dPa·s of 1,695° C. or less. This is considered to allow a large numberof glass sheets to be produced at low cost with high productivity.

Subsequently, ion exchange treatment was performed through immersion ina KNO₃ molten salt (having no history of being used) at 430° C. for 4hours for each of the samples both surfaces of each of which had beensubjected to optical polishing. After completion of the ion exchangetreatment, the surface of each of the samples was washed. Then, thestress compression value (CS₁) and thickness (DOL₁) of a compressionstress layer in the surface were calculated from the number ofinterference fringes and each interval between the interference fringes,the interference fringes being observed with a surface stress meter(FSM-6000 manufactured by Toshiba Corporation). In the calculation, therefractive index and optical elastic constant of each of the sampleswere set to 1.50 and 31 [(nm/cm)/MPa], respectively. It should be notedthat the glass compositions of a surface layer of glass before and aftertempering treatment are different from each other microscopically, butthe glass composition of the glass as a whole is not substantiallychanged after the tempering treatment as compared to that before thetempering treatment.

In addition, ion exchange treatment was performed through immersion in aKNO₃ molten salt (containing 20,000 ppm (by mass) of Na ions) at 430° C.for 4 hours for each of the samples both surfaces of each of which hadbeen subjected to optical polishing. After completion of the ionexchange treatment, the surface of each of the samples was washed. Then,the stress compression value (CS₂) and thickness (DOL₂) of a compressionstress layer in the surface were calculated from the number ofinterference fringes and each interval between the interference fringes,the interference fringes being observed with a surface stress meter(FSM-6000 manufactured by Toshiba Corporation). In the calculation, therefractive index and optical elastic constant of each of the sampleswere set to 1.50 and 31 [(nm/cm)/MPa], respectively.

As evident from Tables 1 to 8, when each sample was subjected to ionexchange treatment in the KNO₃ molten salt free of a history of beingused, its compression stress layer had a compression stress value offrom 812 to 909 MPa and a thickness of from 27 to 40 μm. In addition,when each sample was subjected to ion exchange treatment in the KNO₃molten salt comprising 20,000 ppm (by mass) of Na ions, its compressionstress layer had a compression stress value of from 598 to 695 MPa and athickness of from 25 to 38 μm. Further, the CS₂/CS₁ is from 0.71 to0.80, indicating that the ion exchange performance does notsignificantly change even when a deteriorated KNO₃ molten salt is used.

INDUSTRIAL APPLICABILITY

The tempered glass and tempered glass sheet of the present invention aresuitable for a cover glass for a cellular phone, a digital camera, aPDA, or the like, or a glass substrate for a touch panel display or thelike. Further, the tempered glass container of the present invention issuitable for a container for pharmaceuticals. In addition, the temperedglass and tempered glass sheet of the present invention can be expectedto find use in applications requiring high mechanical strength, forexample, a window glass, a substrate for a magnetic disk, a substratefor a flat panel display, a cover glass for a solar battery, a coverglass for a solid image pick-up element, and tableware, in addition tothe above-mentioned applications.

REFERENCE SIGNS LIST

-   -   1 protective resin film    -   2 glass sheet to be tempered

The invention claimed is:
 1. A tempered glass having a rectangular shapeand having a compression stress layer in a surface thereof, a protectiveresin film being attached to at least one surface thereof, two parallelsides of the protective resin film protruding beyond the tempered glass,and the other two parallel sides of the protective resin film notprotruding beyond the tempered glass, the tempered glass comprising as aglass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% ofAl₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 1.9% of K₂O, andbeing substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 2. The temperedglass according to claim 1, comprising as a glass composition, in termsof mol %, 50 to 80% of SiO₂, 6.5 to 12.4% of Al₂O₃, 0 to 1% of Li₂O, 9to 15.5% of Na₂O, 0 to 1.9% of K₂O, 0.1 to 2.5% of MgO, and 0 to 2.5% ofMgO+CaO+SrO+BaO, and being substantially free of As₂O₃, Sb₂O₃, PbO, andF.
 3. The tempered glass according to claim 1, comprising as a glasscomposition, in terms of mol %, 50 to 80% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 0.01 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to1.9% of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, and 0.1 to2.5% of MgO+CaO+SrO+BaO, and being substantially free of As₂O₃, Sb₂O₃,PbO, and F.
 4. The tempered glass according to claim 1, comprising as aglass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 1 to 15% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 1.9%of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% ofMgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, andbeing substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 5. The temperedglass according to claim 1, comprising as a glass composition, in termsof mol %, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 1.9% of K₂O, 9 to 16.5% ofLi₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratioMgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2, and beingsubstantially free of As₂O₃, Sb₂O₃, PbO, and F.
 6. The tempered glassaccording to claim 1, comprising as a glass composition, in terms of mol%, 50 to 77% of SiO₂, 6.5 to 12.4% of Al₂O₃, 1 to 10% of B₂O₃, 0 to 1%of Li₂O, 9 to 15.5% of Na₂O, 0 to 1.9% of K₂O, 9 to 16.5% ofLi₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% of MgO+CaO+SrO+BaO, and13 to 18.5% of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO, having a molar ratioMgO/(Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO) of from 0.01 to 0.2 and a molarratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and being substantiallyfree of As₂O₃, Sb₂O₃, PbO, and F.
 7. The tempered glass according toclaim 1, wherein the tempered glass has a density of 2.45 g/cm³ or less.8. The tempered glass according to claim 1, wherein when the temperedglass is immersed in a 10 mass % aqueous hydrochloric acid solution at80° C. for 24 hours, a mass reduction, which is a value obtained bysubtracting a mass of the tempered glass after the immersion from a massof the tempered glass before the immersion and dividing a result of thesubtraction by a surface area of the tempered glass before theimmersion, is 40 mg/cm² or less.
 9. The tempered glass according toclaim 1, wherein a compression stress value of the compression stresslayer is 300 MPa or more, and a thickness of the compression stresslayer is 10 μm or more.
 10. The tempered glass according to claim 1,wherein the tempered glass has a liquidus temperature of 1,200° C. orless.
 11. The tempered glass according to claim 1, wherein the temperedglass has a liquidus viscosity of 10⁴⁰ dPa·s or more.
 12. The temperedglass according to claim 1, wherein the tempered glass has a temperatureat 10⁴⁰ dPa·s of 1,300° C. or less.
 13. The tempered glass according toclaim 1, wherein the tempered glass has a thermal expansion coefficientin a temperature range of from 30 to 380° C. of 90×10⁻⁷/° C. or less.14. A tempered glass sheet, comprising the tempered glass according toclaim
 1. 15. The tempered glass sheet according to claim 14, wherein thetempered glass sheet has a length dimension of 500 mm or more, a widthdimension of 300 mm or more, and a thickness of from 0.1 to 2.0 mm. 16.The tempered glass sheet according to claim 14, wherein the temperedglass sheet is formed by an overflow down-draw method.
 17. The temperedglass sheet according to claim 14, wherein the tempered glass sheet isused for a touch panel display.
 18. The tempered glass sheet accordingto claim 14, wherein the tempered glass sheet is used for a cover glassfor a cellular phone.
 19. The tempered glass sheet according to claim14, wherein the tempered glass sheet is used for a cover glass for asolar battery.
 20. A tempered glass container, comprising the temperedglass according to claim
 1. 21. A glass to be tempered having arectangular shape, a protective resin film having a rectangular shapebeing attached to at least one surface thereof, two parallel sides ofthe protective resin film protruding beyond the tempered glass, and theother two parallel sides of the protective resin film not protrudingbeyond the tempered glass, the tempered glass sheet comprising as aglass composition, in terms of mol %, 50 to 77% of SiO₂, 6.5 to 12.4% ofAl₂O₃, 1 to 10% of B₂O₃, 0 to 1% of Li₂O, 9 to 15.5% of Na₂O, 0 to 1.9%of K₂O, 9 to 16.5% of Li₂O+Na₂O+K₂O, 0.1 to 2.5% of MgO, 0.1 to 2.5% ofMgO+CaO+SrO+BaO, and 13 to 18.5% of Li₂O+Na₂O±K₂O+MgO+CaO+SrO+BaO,having a molar ratio MgO/(Li₂O+Na₂O±K₂O+MgO+CaO+SrO+BaO) of from 0.01 to0.2 and a molar ratio (Al₂O₃+B₂O₃)/SiO₂ of from 0.15 to 0.30, and beingsubstantially free of As₂O₃, Sb₂O₃, PbO, and F, the tempered glass sheethaving a density of 2.45 g/cm³ or less, a compression stress value of acompression stress layer of 300 MPa or more, a thickness of thecompression stress layer of 10 μm or more, a liquidus temperature of1,200° C. or less, and a thermal expansion coefficient in a temperaturerange of from 30 to 380° C. of 90×10⁻⁷/° C. or less.
 22. A glass to betempered having a rectangular shape, a protective resin film having arectangular shape being attached to at least one surface thereof, twoparallel sides of the protective resin film protruding beyond thetempered glass, and the other two parallel sides of the protective resinfilm not protruding beyond the tempered glass, the glass comprising as aglass composition, in terms of mol %, 50 to 80% of SiO₂, 5 to 30% ofAl₂O₃, 0 to 2% of Li₂O, 5 to 25% of Na₂O, and 0 to 1.9% of K₂O, andbeing substantially free of As₂O₃, Sb₂O₃, PbO, and F.
 23. The glass tobe tempered according to claim 22, wherein when the glass to be temperedis immersed in a 10 mass % aqueous hydrochloric acid solution at 80° C.for 24 hours, a mass reduction, which is a value obtained by subtractinga mass of the glass to be tempered after the immersion from a mass ofthe glass to be tempered before the immersion and dividing a result ofthe subtraction by a surface area of the glass to be tempered before theimmersion, is 40 mg/cm² or less.
 24. The glass to be tempered accordingto claim 22, wherein the glass to be tempered has a ratio CS₂/CS₁ of acompression stress value CS₂ to a compression stress value CS₁ of 0.7 ormore, the compression stress value CS₁ being determined for acompression stress layer that is obtained by subjecting the glass to betempered to ion exchange treatment in a potassium nitrate molten saltfree of a history of being used, the compression stress value CS₂ beingdetermined for a compression stress layer that is obtained by subjectingthe glass to be tempered to ion exchange treatment in a potassiumnitrate molten salt comprising 20,000 ppm by mass of Na ions.